1. Technical Field
The present invention relates to a control method of a media conveyance device that conveys a continuous medium with slack in the conveyance path of the medium. The invention also relates to a media conveyance device and a printer that convey media by the control method.
2. Related Art
A media conveyance device that conveys continuous media is described in JP-A-2014-141339. The media conveyance device in JP-A-2014-141339 has a delivery mechanism that delivers media; a conveyance mechanism that conveys the media delivered from the delivery mechanism; and a slack chamber (space) between the delivery mechanism and conveyance mechanism. The media conveyance device has a detection mechanism that detects the portion of the media hanging slack in the slack chamber, and a conveyance controller that controls driving the delivery mechanism and conveyance mechanism.
The detection mechanism has a first emitter that emits a first detection beam; a second emitter located below the first emitter and emitting a second detection beam; a third emitter located below the second emitter and emitting a third detection beam; and a fourth emitter located below the third emitter and emitting a fourth detection beam. The detection mechanism also has a first photodetector able to detect a first detection beam that past through the slack chamber; a second photodetector located below the first photodetector and able to detect a second detection beam that past through the slack chamber; a third photodetector located below the second photodetector and able to detect a third detection beam that past through the slack chamber; and a fourth photodetector located below the third photodetector and able to detect a fourth detection beam that past through the slack chamber. The first emitter, second emitter, third emitter and fourth emitter are arrayed vertically at a uniform spacing. The first photodetector, second photodetector, third photodetector and third photodetector are arrayed vertically at a uniform interval. The gaps between the emitters, and the gaps between the photodetectors, are the same.
When driving the conveyance mechanism and conveying the media, the conveyance controller drives the delivery mechanism based on output from the photodetectors of the detection mechanism. More specifically, based on whether or not the detection beam was detected by each photodetector (whether or not part of the media is blocking the detection beam), the conveyance controller can determine how much slack there is in the slack chamber. When the amount of slack gets too small, the conveyance controller drives the delivery mechanism to deliver media so that the media goes slack inside the slack chamber.
If the gap between the emitters and the gap between the photodetectors in the detection mechanism described in JP-A-2014-141339 is small, the amount of slack in the media can be detected with good precision. If the amount of slack in the media is precisely detected, the media can be reliably conveyed with slack between the delivery mechanism and conveyance mechanism, and excessive tension working on the medium can be prevented. As a result, the medium can be conveyed with good precision.
However, because the detection beam emitted from the emitters is diffuse light, if the gap between the emitters and the gap between the photodetectors is small, the second photodetector may detect the first detection beam, the first photodetector and the third photodetector may be detect the second detection beam, and detection beam detection errors may occur. If a detection beam is wrongly detected, the amount of slack in the media cannot be accurately detected.
An objective of the invention is therefore to provide a control method of a media conveyance device able to accurately detect media slack by a detection mechanism having multiple emitters and multiple photodetectors located opposite the emitters. A further objective is to provide a media conveyance mechanism and printer configured to convey media by the control method.